"This has been processed to near oblivion," Adams said. "And it's time to move forward."

The new ordinance would outlaw the bags at checkstands of grocery stores with $2 million or more in annual gross sales and of retailers that have a pharmacy and at least 10,000 square feet, such as Target and Rite Aid.

The mayor first raised the idea of limiting plastic bags at city checkstands in 2008. Then last July, he stood before a rally outside City Hall -- with supporters dressed as shaggy "bag monsters" -- and promised to begin drafting an ordinance. But he backed off after state legislators persuaded him to give their effort a chance.

Senate Bill 536 would have banned the bags at many stores, plus required a 5-cent fee for paper sacks to encourage shoppers to switch to reusable bags. But despite early momentum, the bill was long dead by the time legislators adjourned.

The idea of getting rid of the bags has grabbed attention here and elsewhere in recent years. Critics say the bags are an environmental hazard -- ending up in waterways where they hurt marine life and clogging recycling machines never meant to handle them.

A few dozen U.S. cities now outlaw the bags, following San Francisco, which got rid of them in 2007. Bellingham, Wash., banned them just this past Tuesday. Whole Foods dropped them companywide in 2008, and Fred Meyer last year expanded a paper-only test to 10 Portland stores.

But bag manufacturers and some retailers and customers like the bags; they're cheaper than paper, don't involve cutting trees and are convenient for picking up pet waste and other uses. Supporters also note that some are made of biodegradable materials or can be recycled.

Hilex Poly, a major U.S. manufacturer of plastic bags, called Portland's proposed ban expected but "bad public policy."

"Hilex Poly is committed to working with the recycling industry, policy-makers and other stakeholders to develop a statewide recycling solution -- and that's where the company's focus is at this time," spokeswoman Anna Richter Taylor wrote Thursday in an email.

Portland's ordinance would be the first in Oregon. It would exempt the plastic grocery bags used for produce, bulk food and meat. Pharmacies could use the bags for prescriptions to protect privacy. Low-income Portlanders and seniors may be eligible for free reusable shopping bags from the city, too.

The law would not carry a 5-cent tax on paper bags, but it wouldn't prevent retailers from charging a fee.

For Adams, the ordinance offers a chance to bolster Portland's reputation for environmental friendliness -- and to burnish his green credibility for an expected run for re-election in 2012.

The City Council plans to vote on the ordinance next week; because it's an "emergency" ordinance, it will require a unanimous vote. Adams would be unlikely to unveil such a proposal without council support lined up, however. Voters could seek to overturn the ban through an initiative, but not until May 2012, when the next city election is held.

An environmental group Thursday applauded the mayor.

"This is a critical issue not just for the city but the state and the whole country," said Ben DuPree, a spokesman for Oregon League of Conservation Voters.

A sponsor of the state measure -- Sen. Mark Hass, D-Beaverton -- said he would have preferred a statewide approach to a patchwork of local ordinances. But he supports the mayor's move: "I'm for anything that gets those bags off our roads, out of our rivers and off our beaches."